The invention relates to an internal geared machine, especially an internal geared pump. Such machines are known from numerous publications, for example EP 0 563 661 A1 and its counterpart. U.S. Pat. No. 5,354,188, which is incorporated by reference herein.
Said pump has axially moving discs, so-called axial discs bordering on the rotating toothed parts of the internal toothed ring gear and the pinion. Said axial discs are movable in axial direction. They are pressed against the rotating toothed parts by means of an axial pressure derived from the working pressure so as to compensate the gap between the housing and the toothed part.
With frequency converters a constant displacement pump can be turned into a variable capacity pump by means of speed control. Such a pump has considerable advantages over a variable piston pump. The noise level during operation is much lower, it has a longer service life and uses less energy.
Problems always arise when machines of the above described type have to operate in reverse and when the pressure range changes. For example, there are numerous applications where it is desirable to have an internal geared pump operating both clockwise and counterclockwise. So far, no solution has been found for the cases where such a pump has to operate in a closed circuit.
For high pressure applications an axial compensation is also required. Both axial pressure surfaces of said axial discs are pressurized at the same time. The side connected with high pressure is pressurized with high pressure and the other side is pressurized with the feeder pressure, which is approx. 10 bar.